1. Field of the Invention
The present invention relates to a camera having an automatic focusing device which is capable of enabling two objects on different points to be photographed in a focused condition.
2. Related Background Art
The same applicant has proposed, in Japanese Patent Application No. 236841/1987 corresponding to a U.S. patent application filed on Sept. 28, 1987, a camera having an automatic focusing device which is capable of enabling two objects on different points to be photographed in a focused condition. In this camera, an intermediate lens position is determined between a first lens position where a first object A is focused and a second lens position where a second object B is focused, by dividing the distance between the the first and second lens positions at an appropriate ratio. Then, the amount of defocus between the first and the second lens positions is divided by circle of least confusion so that an aperture value is determined so as to enable the objects A and B to fall within the depth of focus of the lens positioned at the intermediate lens position, thereby ensuring that these objects are photographed in focused condition.
The lens position control system employed in the camera of the type mentioned above is designed to determine the intermediate lens position on the basis of the defocus amount between the first and the second lens positions where the first and the second objects are focused, by dividing the defocus amount at a suitable ratio. Therefore, when either the first lens position where the object A is focused or the second lens position where the object B is focused cannot be detected, the focus control system cannot determine the intermediate lens position, thus failing to shift the lens to such an intermediate lens position. In such a case, the user cannot photograph both objects in focused condition.
For instance, when the lens at the first lens position focusing the object A is driven by an amount equal to the defocus amount obtained by focusing the object B, the lens may be stopped by the closest limit before the lens travels the distance corresponding to the defocus amount. In such a case, the amount of defocus between the first lens position focusing the object A and the stopped lens position (closest limit) obtained during driving the lens for focusing the object B is different from the defocus amount between the first and the second lens positions focused at the first and the second objects A and B. Consequently, the lens cannot be driven to the intermediate lens position which is the position dividing the defocus amount determined by focus detections on two objects, thus failing to accomplish the desired photographing.
The camera of the type described also encounters a difficulty in photographing these two objects A and B when the amount of defocus between these objects is large, i.e., when these objects are largely spaced apart from each other.